PRINCE Harry's protection officers cannot intrude into his social life, Britain's top policeman has said as he was quizzed over the nude photos of the third-in-line to the throne.

Metropolitan Police commissioner Bernard Hogan-Howe told lawmakers that the police who guard Britain's royal family would be crossing a "golden line" if they intervened in their personal lives.

The grainy camera-phone pictures of 27-year-old Harry cavorting naked with a mystery woman during a wild party in a Las Vegas hotel suite appeared on a US celebrity gossip website last month before spreading online.

The affair has hugely embarrassed the royal family and raised questions about why Harry's protection officers, who are supplied by the Metropolitan Police, did not step in when he stripped and revellers took photos.

Mr Hogan-Howe said Scotland Yard were reviewing what had happened.

"Our role is to maintain the security of our protected individual," he told parliament's Home Affairs Select Committee.

"They have to lead a normal life and we have to strike a balance between intrusion into their life and keeping them safe.

"There is a golden line that cannot be crossed, which is getting involved in the social lives of the principals."

He added: "There was nothing inappropriate and what appeared in photographs to be wrong was not as appeared."

Harry, a military helicopter pilot, has since been deployed to Afghanistan for a second tour of duty.

He is set to serve four months as an Apache helicopter pilot at Camp Bastion in southern Afghanistan's restive Helmand Province.

The Taliban said Monday it was determined to kill the prince, who has returned to Afghanistan four years after his first deployment was cut short over security concerns.